Conventional mechanical and electromechanical systems sometimes utilize rotational movement in association with drive path configurations. For example, European Patent No. EP 0 913 600 A1 discloses a system that sets a shaft in a rotational movement via several drive paths. The use of several drive paths driven independently of each other serves in this case essentially to create a redundancy of the overall drive system in order that, if one drive path fails, the shaft can continue to be rotated by the other remaining drive paths. Such so-called “redundant drives” have been implemented in association with increased safety requirements, such as in aircraft construction or the like. The disadvantage of conventional redundant drives is that as a rule such devices require a relatively large amount of space and possess a relatively high number of mobile parts.
In order to remove this disadvantage, it is already known to use planet pinion drives according to the preamble. Such drives are depicted, for example, in British Patent GB 610746 and U.S. Pat. No. 4,898,582. With such drives it is provided that when one drive path fails the other drive path remaining in each case can “take over” the rotation of the shaft. The remaining drive path can be started immediately after the other drive path has failed, without a coupling or the like having to be changed for this purpose. In both the named documents it is however still provided that only one of the two drive paths is operating while the other is at rest.
One conventional method of operation is disclosed in DE 20 012 242 U1. Here the torque is essentially transmitted by the second drive path to the shaft, while the first drive path is used merely to compensate for and correct an error in the speed or torque of the other drive path. The main load is thus permanently borne by the second drive path, while the first drive path is connected for correction purposes only when needed, but must then work at very different speeds. The disadvantage of the method of operation disclosed in DE 20 012 242 U1 is that the individual drive paths are loaded at very varying forces and also non-uniformly, which leads to a clear reduction of their life. However, this is precisely what is not desirable in the case of drives in which redundancy plays an important part.